1. Field of the Invention
This invention relates to face and barrel-type commutators for electric motors and a method of manufacturing such commutators.
2. Description of Related Art
Electric motors and their construction are generally well known. U.S. Pat. No. 5,434,463 relates to a representative direct current motor which utilizes a commutator in combination with crescent shaped brushes. The disclosure of U.S. Pat. No. 5,434,463 is incorporated herein by reference.
U.S. Pat. No. 5,095,611 relates to a method of assembling an electric motor to eliminate a separate end play adjustment wherein permanent magnets act on the armature laminations to urge the motor shaft in one direction so that the entire end play appears at only one end of the shaft. The disclosure of U.S. Pat. No. 5,095,611 is incorporated herein by reference.
Commonly assigned, concurrently filed application entitled Combined Armature and Structurally Supportive Commutator for Electric Motors, the disclosure of which is incorporated herein by reference, is directed to a novel combined armature and structurally supportive commutator wherein all rotational torque is transmitted from the armature to the commutator and to the rotor shaft. Commonly assigned, concurrently filed application entitled Commutator for Two Speed Electric Motor and Motor Incorporating Same, the disclosure which is incorporated herein by reference, is directed to a novel commutator for use in two speed motors, which minimizes the axial space utilized by the commutator.
The manufacture of commutators for such electric motors according to presently known methods generally involves directing a copper strip through a multislide to form a copper shell with notching and skiving processes provided or in existing flat commutators, through progressive die forming. The formed shell is then transferred to a molding operation for the purpose of manufacturing the supporting body by molding phenolic material directly to the shell. Thereafter certain secondary operations are performed, as for example, to produce slots in the shell following the molding and post curing procedures to bake the commutator.
Bar separation processes typically utilize a saw cut operation which inevitably leaves metal particulates in the slots thus created, thereby requiring brushing of the slots to remove the metal particulates. Furthermore, the step of molding phenolic material directly to the shell inevitably leaves residues of phenolic material on the tangs of the commutator which generally requires further brushing operations to clean the surfaces such that they may be suitable for fusing processes during the manufacture of the final motor product.
U.S. Pat. No. 4,481,439 relates to a molded commutator made up of segments arranged in a ring with their brush contact surfaces facing inwardly and forming a cylindrical shape. A matrix of plastic is molded between and around the outside of the segment ring in order to separate the segments electrically and to hold them in the ring configuration.
U.S. Pat. No. 4,663,834 relates to a method for making an inverted commutator assembly for mounting on a rotor shaft, comprising forming a plurality of rotatable commutator segments with each segment having a brush contact surface into a ring in which the segments are circumferentially arranged in a spaced-apart relationship about a longitudinal access of rotation, and placing reinforcing means in the form of an outer casing of high tensile strength material around the longitudinal axis of rotation for reinforcing the segments. A matrix of insulating material is molded between the inside of the casing and the outside of the ring of segments and between the segments for electrically isolating the segments. Means for affixing the commutator assembly to a rotatable shaft passing through the longitudinal access of rotation is then attached to the matrix.
U.S. Pat. No. 4,349,759 relates to a commutator for electrical machines and a method of manufacture of the commutator in which the commutator consists of a lamination assembly held together by a pair of shrink-rings. One of the rings serves to support the commutator on a commutator hub and comprises first and second ring portions having between them a decoupling portion. The first ring portion is in the form of a shrink-ring and holds together the lamination assembly. The second ring portion is secured to the commutator hub. The other shrink-ring also holds together the lamination assembly. In the method of manufacture of the commutator, both the first and second ring portions are simultaneously shrunk on to the lamination assembly and commutator hub respectively.
The presently known techniques for manufacturing commutators clearly involve well known manufacturing procedures which are generally time consuming and expensive, particularly in that relatively large sections of the manufacturing material must be processed through numerous steps to produce the final commutator, with consequent excessive loss of material. Such material losses are particularly caused generally by the cutting operations and the operations requiring the removal of materials and therefore generally result in substantially increased costs to manufacture the commutators. The present invention is directed to a unique method for manufacturing commutators for electric motors whereby such intricate and expensive manufacturing operative steps are minimized, with the result that improved commutators are produced at reduced cost for incorporation into electric motors of various types.
The invention relates to a method of manufacturing a commutator adapted to be mounted on a shaft of an electric motor for cooperation with electrically conductive brushes of the motor, which comprises molding a support member from an electrically insulating material, the support member having a major outer surface portion divided into subsections of lesser area by a plurality of rib members extending upwardly from said outer surface portion, cutting a sheet of electrically conductive material into commutator segments of predetermined shape and dimensions for attachment to the outer surface portions of said subsections, and attaching the commutator segments to the outer surface portions of the subsections such that the segments form respective commutator surfaces interrupted by the rib members. The support member has a generally annular disc-like configuration and the major outer surface portion has a generally annular configuration. The rib members extend in a generally radial direction along the major outer surface portion. The rib members have a heightwise dimension above the major outer surface slightly less than the thickness of the commutator segments such that when the commutator segments are attached to the outer surface portions of the support member, the outer surface of the commutator is provided with insulating gaps between adjacent pairs of commutator segments.
According to the method, the support member is molded from a high temperature resinous material, preferably a phenolic resinous material. Further the commutator segments are cut from a suitable copper alloy sheet material and the step of attaching the commutator segments to the outer surface portions of the subsections utilizes adhesive means such a suitable high temperature acrylic adhesive, in which case the thickness of the commutator segments will include the relatively thin layer of adhesive. The commutator segments each further comprise a hook-shaped member extending therefrom and adapted to be connected to armature winding means of the motor. In one embodiment, the hooks extend from one side of the support member to the other side thereof over the outer periphery of the support member. For certain applications, the hooks extend through apertures in the support member.
In another embodiment a method of manufacturing a barrel-type commutator is disclosed wherein the support member has a generally cylindrical configuration and the major outer surface portion is generally cylindrical. In this embodiment, the rib members extend upwardly from the generally cylindrical outer surface portion and have a heightwise dimension slightly less than the thickness of the commutator segments such that when the commutator segments are attached to the outer surface portions of the support member, the respective outer surface of each segment is slightly higher than the upper surface of each adjacent rib member. The support member is molded from a high temperature resinous material such as a phenolic resinous material. Furthermore, in this embodiment, the step of attaching the commutator segments to the outer surface portions of the subsections also utilizes adhesive means such as a high temperature acrylic adhesive as described previously. A hook-shaped member also extends from each segment and is adapted to be connected by fusing or crimping to armature winding means of the motor.
A commutator adapted to be mounted on a rotatable shaft of an electric motor for cooperation with electrically conductive brushes of the motor is also disclosed, which comprises a support member molded from an electrically insulating material, the support member having a major outer surface portion divided into subsections of lesser area by a plurality of upstanding radially extending rib members on the outer surface portion. A plurality of commutator segments of predetermined shape and dimensions are attached to the outer surface portions of the subsections.
The invention also relates to an electric motor which comprises, a housing, a rotor positioned within the housing and including, a rotor shaft rotatably mounted within the housing, an armature core having armature windings wound therearound, and a commutator for directing electric current from a plurality of electrically conductive brushes to the armature windings. The commutator includes a support member molded from an electrically insulating material and having a major outer surface portion divided into subsections of lesser area by a plurality of rib members extending upwardly from the outer surface portion. As described in connection with the commutator, a plurality of commutator segments of predetermined shape and dimensions are attached to the outer surface portions of the subsections, preferably by adhesive means.